Recently, various functions such as radio frequency identification (RFID), near field communication (NFC), wireless power charging (WPC), an interactive pen tablet function, and the like have been added to portable terminals such as cellular phones, table PCs, and the like.
NFC refers to a technique in which data is transmitted between terminals at a close distance of 10 cm using a non-contact type near field communication module that uses a 13.56 MHz frequency band as one of RFIDs which are electronic tags. NFC is being widely used not only for mobile payment but also for a device for transmitting good information or travel information to visitors in supermarkets and general stores using a file transferring method, a transportation device, an access control lock device, and the like.
Also, in “Android Beam,” which is provided in smart phones recently announced by Google, a mobile payment function and a function of transferring photos, business cards, files, maps, web sites, etc. from one phone to another are provided as NFC-based short-range information transmitting and receiving functions.
In addition, a wireless charging function for charging an embedded battery in a wireless manner is provided in a portable terminal. The wireless charging function is performed by a wireless power receiving module embedded in the portable terminal and a wireless power transmitting module which supplies power to the wireless power receiving module.
Recently, a hybrid-type (combo-type) antenna unit including an antenna for NFC and a Wireless Power Consortium (WPC) (or Alliance for Wireless Power (A4WP)) antenna for wireless charging of a battery is installed in a portable terminal such as a smart phone or the like.
Since such a hybrid-type antenna unit uses a magnetic field, a magnetic field ranging from 100 kHz to tens of MHz is generated in a process of performing near field communication with an adjacent portable terminal or in a process of performing a wireless charging function for charging a battery.
Accordingly, in a wireless power transfer module to which the hybrid-type antenna unit is applied, a magnetic field shielding sheet in which a first magnetic sheet and a second magnetic sheet are stacked is used, and thus performance of near field communication and performance of wireless charging are simultaneously improved.
In a process of manufacturing a magnetic field shielding sheet through a stamping process after stacking a first magnetic sheet and a second magnetic sheet, a stamped surface is exposed. When the magnetic field shielding sheet is applied to a product in a state in which the stamped surface is exposed to the outside, a problem that micro-pieces are separated from the stamped surface to short-circuit an electronic circuit occurs.
Meanwhile, currently, a salt spray test, which is a type of reliability test, is being strengthened to test reliability of electronic products such as portable terminals and the like.
Accordingly, when the shielding sheet is made of a magnetic material including a metal component, there is a problem in that the exposed surface is oxidized due to a penetration of moisture or the like when a reliability test is performed so that the shielding sheet fails to pass the reliability test.